The present invention relates to a current detection device, a method for detecting electric current flowing through an electric circuit employed in an equipment such as an automotive vehicle, and a power supply system using the same.
In recent years, due to wide spread of electric vehicles and hybrid cars, etc., a highly sophisticated current detection device is demanded with a view to managing a charging or discharging state of a battery. It has heretofore been proposed to provide such a current detection device which employs a standard resistor to allow electric current to flow to cause a voltage drop which is measured to detect the magnitude of electric current. Such a current detection device encounters an increase in the size and weight of the standard resistor, with resultant remarkable increase in the amount of heat especially when electric current flowing through the standard resistor increases. Accordingly, the aforementioned current detection device is not suited for use in an electric junction box to perform distribution of electric power output in the automotive vehicle.
To address such an issue, it has heretofore been proposed to provide a current detection device adapted to detect electric current with the use of a current transformer and a Hall element of a magnetic reluctance type, a typical example of which is disclosed in Japanese Patent Provisional Publication No. 59-79860. The current detection device of such a type requires an annular core of a size to suit the magnitude of electric current to be measured, resulting in a difficulty caused in reducing the volumetric size and weight of the device.
To improve such a difficulty, it has also been proposed to provide a current detection device which detects electric current without the use of the magnetic core, an example of which is disclosed in Japanese Patent Publication No. 8-3499. This current detection device has a structure wherein a circuit substrate is formed with a central bore through which a linear electric conductor extends and wherein two magneto-electric transducer elements are located in a circumferential region around the central bore of the substrate for detecting electrical current. Electrical signals produced by the two transducer elements are synthesized, allowing the device to produce an output with the magnitude twice times that of the single magneto-electric transducer element.
However, since the magnitude of the output signal produced by such a current detection device is extremely low level, it is required for the current detection device to produce an output signal with a further increased level. With such a structure, further, a special advance work is required for passing the linear electric conductor to be measured through the circuit substrate, resulting in a poor workability of the current detection device in a mounting process. Also, in the current detection device equipped with the magneto-electric transducer elements, the presence of plural electric conductors accommodated in the electrical junction box renders the current detection device to suffer a difficulty in accurately detecting electric current owing to interference of magnetic flux disturbances caused by electric current flowing through the plural conductors.
It is therefore an object of the present invention to provide a current detection device, a method for detecting electric current and a power supply system using the same which enable electric current flowing through en electric conductor to be accurately detected and which provide an ease of assembling of the current detection device at a low cost.
According to a first aspect of the present invention, there is provided a current detection device which comprises an electric conductor placed in a plane and having first, second and third conductor components extending from a common diverging point in three orientations with a given angle with respect to one another, first and second magnet-electric transducer elements located at both sides of the first conductor component in positions equally spaced from the first conductor component and in the vicinity of the diverging point for producing first and second electric signals in response to magnetic fluxes caused by electric currents flowing through the first, second and third conductor components, with each transducer element having a flux sensitive surface aligned in the plane of the electric conductor, and a calculation processor circuit responsive to a differential value between the first and second electric signals for thereby detecting electric current flowing through the first conductor component.
According to the first aspect of the present invention, the presence of the first and second magneto-electric transducer elements located at both sides of the first conductor component in the vicinity of the diverging point for enabling electric current flowing through the first conductor component to be detected on the basis of a differential value between first and second electric signals produced by the first and second magneto-electric transducer elements. Since, in this instance, each of the two magneto-electric transducer elements undergoes an influence of the magnetic fluxes caused by electric current flowing at a position upstream of the diverging point and electric current at a position downstream of the diverging point, each of the transducer elements performs magneto-electric conversion of a larger amount of magnetic fluxes than that of a case wherein electric current flows through the single linear conductor. As a result, even when the magnitude of electric current flowing through the first conductor component remains at a small value, it is possible to detect current with a high sensitivity.
Further, even when there are magnetic flux disturbances in the vicinity of the current detection device, the presence of the differential value between the electric signals of the two transducer elements renders cancellation of the magnetic flux disturbances. As a result, even when there are other electric conductors placed in juxtaposition with the first conductor component, the current detection device of the present invention does not suffer from the magnetic flux disturbances, with a resultant capability in highly accurately detecting electric current. Also, with the use of only two magneto-electric transducer elements, it is possible for the current detection device of the present invention to be manufactured at the same price as the state-of-the-art current detection device which also employs the two magneto-electric transducer elements. Further, in the current detection device of the present invention, there is no need for using the flux concentrator core, achieving a miniaturization, reduced weight and low manufacturing cost of the device.
According to a second aspect of the present invention, there is provided a method for detecting electric current, which comprises locating an electric conductor composed of first, second and third conductor components extending from a common diverging point in three orientations angled at a given angle with respect to one anther, locating first and second magnet-electric transducer elements at both sides of the first conductor component in positions equally spaced from the first conductor component and in the vicinity of the diverging point for producing first and second electric signals in response to magnetic fluxes caused by electric currents flowing through the first, second and third conductor components, with each transducer element having a flux sensitive surface aligned in the plane of the electric conductor, and calculating a differential value between the first and second electric signals for thereby detecting electric current flowing through the first conductor component.
According to a third aspect of the present invention, there is provided a power supply system which comprises a current detection device including an electric conductor placed in a plane and having first, second and third conductor components extending from a common diverging point in three orientations with a given angle with respect to one another, first and second magnet-electric transducer elements located at both sides of the first conductor component in positions equally spaced from the first conductor component and in the vicinity of the diverging point for producing first and second electric signals in response to magnetic fluxes caused by electric currents flowing through the first, second and third conductor components, with each transducer element having a flux sensitive surface aligned in the plane of the electric conductor, and a calculation processor circuit responsive to a differential value between the first and second electric signals for thereby detecting electric current flowing through the first conductor component, a battery electrically coupled to the first conductor component, a load electrically connected to the second conductor component, and an electric power generator coupled to the third conductor component, wherein the amount of electric power output of the electric power generator is controlled in response to charging and discharging current, detected by the calculation processor circuit, of the battery flowing through the first conductor component.
An important advantage of the power supply system of the present invention concerns a miniaturization and a low cost of the power supply system owing to the use of the current detection device in miniaturized size and low cost. Also, since it is possible to accurately detect charging and discharging current of the battery with the greatest sensitivity, the electric power generator is enabled to be accurately controlled to provide a desired amount of electric power output.
According to a fourth aspect of the present invention, there is provided a current detection device which comprises a T-shaped electric conductor including first, second and third conductor components formed in a unitary structure, first and second magnet-electric transducer elements located at both sides of the first conductor component in positions equally spaced from the first conductor component and in the vicinity of the diverging point for producing first and second electric signals in response to magnetic fluxes caused by electric currents flowing through the first, second and third conductor components, with each transducer element having a flux sensitive surface aligned in the plane of the electric conductor, a sensor substrate including a calculation processor circuit responsive to a differential value between the first and second electric signals for thereby detecting electric current flowing through the first conductor component, and a case for accommodating the electric conductor, the first ad second magneto-electric transducer elements.
Since an assembly of the current detection device is carried out by merely assembling the T-shaped electric conductor, the first and second magneto-electric transducer elements and the sensor substrate into the case to allow the electric conductor and the sensors to be easily positioned in a high precision to enable an accurate detection of electric current.